Can anyone deny the effects of the expensive Euro periods since 2002 on the economies, exports, tourism, competitiveness and budgets (tax revenues) of many Eurozone members (PIIGS included)? Even these days, when the Euro is worth 1.4 USD!
And what is the effect of that on Chinese exports to the Eurozone? A "flood"! Not to mention US, UK, even Swedish exports to the Eurozone.
And the effects on the tourism of Greece, Portugal, Spain, Italy and other Eurozone members that compete as destinations with neighbouring or distant non Eurozone and non-EU countries/economies.
Let's be honest: In the last 50 or so yrs, being a neighbour of Germany has been a great advantage (exports) for many economies that are mow member of the Eurozone or at least the EU.
In other words, have NL, BEL, DK, FR, SWE, etc not benefited from their proximity to the German market (the perennial steam engine of European growth) compared with eg POR or GR? In many ways, not mere exports. And of course Germany has benefited too from this "integration" due to proximity.
Also, should one go into a Max Weber type of analysis in order to understand the roots of the difference in economic, biz, social and other systemics, eg between NL and POR? In yes.
Plus, as per the "transfer union" soundbites, the bottom line is that yes, a US of E will have de juris to be a transfer union, much like the USA is. Else it's a Catch 22 European union.
PS 1) At its roots Economics, unlike Physics, Chemistry or Maths, is a social science.
PS 2) Do European countries have the same historical traditions and philosophy re eg accounting and audit? IMO, no, these vary considerably. Some cultures focus on the future instead of over-analysing the past, hence have less of a tradition in accounting, stats, etc than other ones!